1. Field of the Invention
The present invention relates to a key switch device and a keyboard wherein a key top is moved up and down relative to a switch panel due to a structural interlock between a pair of link members and the key top.
2. Description of the Related Art
Generally, in a key switch device having a switch mechanism adapted to close or open a contact of an electric circuit due to up-and-down motion (or vertical motion) of a key top, the key top is supported by a pair of link members so as to be moved up and down. There are various types of link members. For example, in a gear link-type, a pair of link members are assembled together into a reverse V-shape as seen laterally and meshed at toothed end regions formed on one end thereof (Japanese Unexamined Patent Publication No. 2003-31067). In a pantograph type, a pair of link members are assembled together into an X-shape as seen laterally and coupled at an intersection so that each link member may rotate or slide relative to each other. The key top may be pressed while a surface of the key top is parallel to a base plate due to interlock between each of the pair of link members. When the key top reaches a lowermost position in an up-and-down stroke thereof, the pair of link members lie under the key top, and when the key top reaches a uppermost position in up-and-down stroke thereof, the pair of link members are raised so as to represent a reverse V-shape or X-shape as seen laterally.
Japanese Unexamined Patent Publication No. 2003-31067, paragraph [0020] explains the configuration of the key switch device. Concretely, it is described that “key switch device 10 has a base 12; a key top 14 having an operation surface 14a to which an operator may carry out key-entry operation, the key top being positioned on surface 12a of base 12 so as to be moved in up-and-down direction; a pair of link members 16 adapted to guide and support key top 14 on base 12 in the up-and-down direction; and a switch mechanism 18 adapted to close and open a contact of an electric circuit corresponding to the motion of key top 14 in the up-and-down direction.”
Japanese Unexamined Patent Publication No. 2003-31067, paragraph [0077] explains the configuration of the key switch device for reducing noise due to an up and down motion of the key top. Concretely, it is described that “in key switch device 110, a pair of assist-support piece 118 may be arranged on base 112 in order to assist the motion of a pair of link member 74 (FIG. 16). Each assist-support piece 118 is arranged at generally an intermediate position between a pair of sliding-engagement portions 114 so as to obliquely project from major surface 112a of base 112, and positioned so that a free end of each assist-support piece 118 opposes each other. Similarly to upright plate portion 114a of sliding-engagement portion 114, assist-support piece 118 may be integrally formed with base 112 by punching a profile of assist-support piece 118 at a predetermined place of base 112 by means of a press machine or the like, and bending the punched portion toward the side of major surface 112a. Each assist-support piece 118 projects above sheet member 58 through a hole (not shown) formed in sheet substrates 50 of membrane sheet 52 and sheet member 58.”
Further, Japanese Unexamined Patent Publication No. 2003-31067, paragraph [0078] explains the function of the pair of assist-support piece 118. Concretely, it is described that “the top surface of a pair of assist-support piece 118 slidably contacts the lower surface of coupling part 82 of link member 74 in the whole up-and-down stroke of key top 72. To this end, each assist-support piece 118 has a meander shape corresponding to the trajectory of movement of coupling part 82 of link member 74. Due to this, the bumpy motion of link member 74, which may occur during the key-entry operation of key top 72, may be effectively reduced and the bumpy motion of key top 72 and noise therefrom may be reduced as possible.”
In the conventional key switch device, it is intended to reduce sound due to the up and down motion of the key top supported by the pair of link members (so-called “chattering noise”). However, it is not intended to reduce “key-entry noise,” which occurs when the operation surface of the key top is relatively strongly pressed by a finger. In this regard, the “key-entry noise” means operation noise which occurs when impact at the time of pressing the key top reaches the base (or switch panel) and rebounds from a membrane sheet or a metal support panel. It has been found that the rebound of the key-entry noise is caused by a gap between the switch panel and the membrane sheet, and/or a gap between the membrane sheet and the support panel.
Generally, in order to integrally stack the switch panel, the membrane sheet and the support panel, a plurality of pins projecting from the back side of the resin switch panel pass through a hole of the membrane sheet and the support panel from the front side of the membrane sheet to the back side of the support panel, and the front end of the pin exposed from the hole is heated and melt on the back side of the support panel. The pins are integrated with the stacked panel/sheet while positioning the switch panel, the membrane sheet and the support panel in a horizontal direction, and located at a periphery of the key top. In a keyboard having a plurality of key switch devices, each pin is positioned between the neighboring key switch devices. Although the stacked panel/sheet does not have a gap near the pin, a gap exists between the upper stack and the lower stack in an area which does not includes the pin.
Although the number of the pins may be increased in order to minimize the gap, there is a structural restriction in this case. Although it may be possible to bond boundary surfaces of the upper and lower stacks by adhesive, the positional accuracy between each layer may be deteriorated. In order to reduce the key-entry noise, soft material may be used for the switch panel and/or an impact absorbing sheet may be used. However, when the switch panel is made from soft material, the manufacturing cost of the switch panel is increased and the dimensional stability thereof is deteriorated. On the other hand, when the impact absorbing sheet is used, the thickness of the key switch device and the keyboard is increased, resulting in that a desired specification for the key switch device or the keyboard cannot be satisfied.
Further, in the conventional key switch device, when liquid is dropped on the device, the liquid may enter a gap between the switch panel and the membrane sheet, the liquid may spread on a boundary surface between the switch panel and the membrane sheet by capillary action, and then the liquid may enter an air vent of the membrane sheet. If the liquid enters the air vent, the liquid may reach the contact of the electric circuit, resulting in contact fault. Further, if the liquid enters within a housing of the keyboard, insulation failure may occur.
In addition, in a key switch device having a rubber dome (or an actuating member) adapted to close a contact of the membrane sheet as the key top is lowered, the switch panel is stacked on the membrane sheet after the rubber dome is bonded to the membrane sheet by adhesive. Therefore, when the positional accuracy of the rubber dome is not good, the positioning of the rubber dome and the switch panel cannot be accurately carried out.
Some of the types of adhesive used to bond the rubber dome to the membrane sheet have poor oil resistance. Although adhesive including fluoro-silicon (fluorinated silicon) having high oil resistance may be used, the cost of fluoro-silicon is high.